The invention relates to a method of transmitting a data stream or message from an FDX (full duplex) transponder to an interrogator or reader capable of reading both FDX and HDX RF-ID systems. The data stream comprising a synchronization section and a data section stored in the FDX transponder device for transmission to an interrogating device in full duplex mode during which the interrogating device is continuously emitting an interrogating command. The receipt of the interrogating command by the transponder device prompts the output of a data message.
Various types of recognition systems are taught by the following commonly assigned U.S. Pat. and Applications: U.S. Pat. Nos. 5,287,112; 5,270,717; 5,196,735; 5,170,493; 5,168,282; 5,148,404; 5,126,745; 5,073,781; 5,053,774; 5,025,492; Ser. No. 08/021,123, filed Feb. 23, 1993; Ser. No. 08/065,286, filed May 21, 1993; and Ser. No. 08/086,786, filed Jul. 2, 1993. Various systems conforming to the teachings of the foregoing documents are marketed under the name TIRIS ("Texas Instruments Registration and Identification System"). A recognition system similar in result to, but structurally and functionally specifically different from, TIRIS is disclosed in U.S. Pat. No. 4,918,955.
In many recognition systems, an interrogator (sometimes called a "transmitter/receiver" or a "reader") selectively radiates energy from a first inductor or antenna. The radiated energy may by itself constitute or may contain an "interrogation signal." In many cases, the interrogation signal is simply an AC burst of energy or an AC signal of a selected frequency and duration. The interrogation signal is received by a second inductor or antenna associated with a transponder (sometimes called a "tag"). The transponder is attached to, embedded or implanted in, or otherwise on or in an object. In response to its receipt of the interrogation signal, the transponder produces a "recognition signal," which typically comprises a code. In some recognition systems, the recognition signal is transmitted by the transponder back to the interrogator via the inductors or antennas. In other systems the interrogation signal itself is selectively loaded according to a code in the transponder. Transponders associated with objects "matching" certain criteria produce predetermined recognition signals. Transponders associated with other objects not matching the criteria may respond to the interrogation signal but transmit recognition signals different from the predetermined recognition signal.
The interrogator includes facilities which analyze the recognition signals to determine which of the analyzed signals are the predetermined recognition signal produced by the matching objects. If an analyzed recognition signal is the predetermined recognition signal, this fact may be utilized by the interrogator or by facilities responsive to the interrogator to cause one or more of a number of events or operations involving the matching objects to occur. If an analyzed recognition signal is not the predetermined recognition signal, such events or operations either do not occur or occur differently.
In an exemplary TIRIS system, transponders may be attached to or implanted in objects which constitute the corpus of living animals, such as steers or hogs. The animals may be counted or not counted, directed or not directed to a specific area or similarly discriminated on the basis of the predetermined recognition signal being produced or not produced in an interrogator by the transponders. Thus, "matching" animals in a group of animals might include those belonging to a specific owner or animals which are of a particular size or age. Similarly, transponders may be attached to commingled luggage in an airport. An interrogator adjacent to a conveyor carrying the luggage effects directing the luggage to the luggage-handling operations of the appropriate airline.
Another environment in which TIRIS recognition systems may be used relates to motor vehicles. One use finds an interrogator associated with the ignition switch of a vehicle and transponders associated with ignition keys. Only a key which includes a transponder "matching" the interrogator and which is capable of operating the ignition switch can effect engine starting.
Another vehicle-related recognition system of the AVI variety finds transponders in authorized vehicles and interrogators located at toll plazas. As an authorized vehicle passes through the plaza without stopping, the interrogator treats the presence of a recognition signal as confirmation of authorization, identifies the vehicle through analysis of the recognition signal, and updates toll charge billing data which is stored in associated facilities. At the end of a billing cycle, the stored billing data is used to prompt periodic payment of cumulated toll charges by the vehicle's owner. The updated billing data may also be sent by the interrogator to the transponder and facilities associated therewith which permit the vehicle's operators to periodically ascertain the current cumulated toll charges ascribable to the vehicle.
Portability and/or space limitations usually result in the interrogator of a TIRIS-type of recognition system being not very powerful. Also, the recognition signals, that is the signals transmitted back to the interrogator from the object-included transponder, may be derived from the limited energy radiated from the interrogator, not from energy derived from an object-contained power source, such as a battery, as is typical in systems of the AVI type. While the use of a battery with object-included circuitry of a TIRIS system is technically possible, the large size and resulting unwieldiness would lead to severe use restrictions--implanting a transponder having a battery in an animal would prove to be difficult and/or costly--or rejection by users--the presence of a battery in a key-included transponder would render the key annoyingly large--.
In TIRIS and other recognition systems wherein the transponder is "batteryless", the interrogation signal from the interrogator may include an RF component. The antenna or inductor of the transponder may be connected to a capacitor in the transponder to form a parallel resonant circuit which resonates at the frequency of such RF component. An energy storage element, such as a storage capacitor connected in series to a diode, may be connected to the resonant circuit, so that energy derived from the RF component of the interrogation signal is stored in the storage capacitor. This stored energy is used to energize the remainder of the transponder, which may be implemented as circuitry on or in one or more chips or integrated circuits. The transponder, therefore, may comprise a very small "package" --the package may be generally cylindrical, with a length of about 1 1/4 inches or less and a diameter of about 1/8 inch or less--which includes the antenna or inductor, the resonant circuit, the energy storage capacitor and the integrated circuit.
Recognition systems may include transponders which include only a resonant circuit, of which the transponder's antenna is the inductor. See U.S. Pat. No. 4,918,955. Such systems may also include transponders generally appropriate for batteryless operation utilizing one or more coding or modulation techniques and/or code modulation. For specific use in recognition systems implementing half-duplex operation, see commonly assigned U.S. patent application Ser. Nos. 08/021,123, 08/065,286 and 08/086,786. For recognition systems using full-duplex operation see commonly assigned U.S. patent application Ser. No. 08/212,123. For systems using both half duplex and full duplex techniques see commonly assigned U.S. patent application Ser. Nos. 08/065,286 and 08/086,786. Other full duplex recognition systems are described in U.S. Pat. No. 4,730,188 issued to Milheiser and U.S. Pat. No. 5,211,129 issued to Taylor et al.
As noted, the transponder package may, inter alia, be implanted in an animal, typically subcutaneously, or placed in other environments which may be hostile to the transponder or to which the transponder may be hostile.
To this end, the transponders are typically placed in glass or plastic tubes to provide protection from damage caused by impact forces incident to dropping or rough handling. The tubes also protect the transponders from hostile environments, such as the body fluids of an animal. The tubes further protect the environment, which may again be the body of an animal, from the deleterious effects which might otherwise be caused by a "foreign body" such as the transponder.
In transmitting a data message from an FDX transponder device to an interrogating device it is usual to proceed on the basis of a specific transmission protocol which precisely defines how the data message is configured. For example, it has been proposed to compose the data message of a synchronization section of a selected number of bits followed by a data section of another selected number of bits which is typically greater than the number of bits in the synchronization section. The synchronization section is required so that the interrogating device receiving the data message can be synchronized to the bit rate and so that the start of the data section, containing the actual information to be transmitted, can be explicitly identified or determined.
One prior art method of identifying the synchronization section, as an example only, is to always use the same bit pattern for this synchronization section of the data message. This technique has the disadvantage, however, that all possible bit patterns can no longer be used in the data section. This is because the same bit pattern might occur in the data section as well as in the synchronization section. In such an event, explicitly establishing the start of the data section in the data message would no longer be possible.
To eliminate such a restriction as regards the content of the data section, another possible technique is to apply the so-called code-violation method in the synchronization section. In this technique, it is assumed that in transmitting the data message the individual bits are output at a prescribed bit rate. To identify the synchronization section 3 bits in direct sequence are replaced by 2 bits. The duration of the 2 bits is greater than the 3 bits, so that the total duration of the 2 bits is the same duration as the duration of the 3 bits. This means that in the synchronization section, 2 bits having a slower bit rate occur with a correspondingly longer duration than the standard bit rate used by the data section. Thus, the interrogating device is able to identify the synchronization section from the occurrence of these bits of longer duration and thus determine or identify where the data section containing the information to be transmitted begins. Which of the 3 bits in the synchronization section has been replaced by 2 bits of longer duration is determined by the transmission protocol selected for the system.
A code violation method wherein three bits are replaced by two bits of longer duration, results however in disadvantages when the data transmission is made in the FDX (full duplex mode) with ASK (amplitude shift keying) modulation. In such a data transmission technique, the interrogation command is continuously transmitted by the interrogating device and the answer or response by the transponder device occurs at the same time so that they overlap in time. "Continuously" in an FDX transmission mode means that the output of the interrogation commands lasts at least as long as the data message (including both the synchronization section and the data section) so that the aforementioned overlap in time occurs. If the carder frequency used is between 130 and 140 KHz (such as, for example 132.2 KHz used by TIRIS) at which the interrogating device outputs the interrogation command and if the bit rates of the data message are within the same range (approx. 136.2 or 132.2 KHz for TIRIS) the spectral components produced by the synchronization bits of longer duration result in a sideband for demodulation which in the interrogating device are overlapped by the carrier frequency such that they extend into the range of phase noise of the transmitted data signals. Demodulation of the data section is made considerable more difficult by this, and in some instances may even be impossible.
Therefore, it is an object of this invention to provide a technique so that the code violation method can be used in a data exchange between a transponder device and an interrogating device in full duplex mode with ASK modulation.